Many forms of electrical load powering apparatus have a load connection, a voltage supply connection and a common, and electronic circuitry which switches the voltage supply connection to an electrical load. Without limiting the intended scope of applications of the invention such as switching regulator power supplies and all other applications to which the features and advantages of the invention commend it, the background of the invention is discussed in regard to a relatively specific example of powering electronically commutated motors.
While conventional brush-commutated DC motors may have numerous advantageous characteristics such as convenience of changing operational speeds and direction of rotation, it is believed that there may be disadvantages, such as brush wear, electrical noise, and radio frequency interference caused by sparking between the brushes and the segmented commutator, that may limit the applicability of such brush commutated DC motors in some fields such as the domestic appliance field. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have the above discussed advantageous characteristics of the brush-commutated DC motors without many of the disadvantages thereof while also having other important advantages. Such electronically commutated motors are disclosed in coassigned Erdman U.S. Pat. Nos. 4,015,182, 4,005,347, 4,169,990, 4,449,079, 4,459,519, 4,513,230, 4,556,827, and 4,654,566 and coassigned Erdman U.S. patent application Ser. No. 015,409 filed Feb. 17, 1987, in coassigned Erdman et al. U.S. Pat. Nos. 4,390,826 and 4,532,459, in coassigned Wright U.S. Pat. No. 4,162,435, in coassigned Boyd U.S. Pat. No. 4,528,485, in coassigned Boyd et al. U.S. Pat. Nos. 4,540,921, 4,636,936 and 4,642,536, in Alley U.S. Pat. No. 4,250,544, Bitting et al. U.S. Pat. No. 4,500,821 and in Young U.S. Pat. No. 4,642,537. All of the foregoing coassigned U.S. Patents are hereby incorporated herein by reference. While the aforementioned coassigned patents and application, for instance, undoubtedly illustrated many features, it is believed that the control circuits for electronically commutated motors in general and for other applications such as switching regulator power supplies could be even further improved, as well as the methods of control utilized therein.
For example, coassigned Alley U.S. Pat. No. 4,250,544 discloses an arrangement for controlling an electronically commutated motor and is incorporated by reference. Switching of the terminals of winding stages of an electronically commutated motor is accomplished by field effect transistors therein. While such circuitry is effective and satisfactory, it is desirable in some applications contemplated for the electronically commutated motors or in power supplies, to switch relatively high voltages including voltages from generally about 100 volts, for example, up to about 400 volts or more to the winding stages. The terminals thus undergo relatively sudden high voltage excursions relative to the common, or ground connection of the electrical load powering apparatus. Such voltages make the inherent or stray capacitances and inductances of circuits for controlling the switching an important consideration. It is believed that when such higher voltages are used, or whenever the inherent capacitance or inductance is significant, the probability of false triggering, lack of reliable or positive switching, and even oscillation is increased.
Circuitry with a transformer with numerous windings for base drive of a low input impedance power transistor is illustrated in Mentler U.S. Pat. Nos. 4,302807 and 4,308,577. Circuitry with three transformers for input drive of a low input impedance power transistor is shown in Yuzurihara U.S. Pat. No. 4,605,865.
Field effect transistors (FETs) and insulated gate transistors (IGTs) have extremely high input impedance and are voltage-controlled devices with an input capacitance which must often be taken into account. Problems of controlling transistors of this type when switching high voltage to a load under transformer drive are of continuing importance to the art, and new ways of overcoming the problems are needed.